There's nothing more frustrating than working your ass off at the gym, counting calories (or macros!) obsessively, and still not seeing the scale budge. You cut out all your favorite junk foods for a reason, right?

Of course, you can't wash down your green juice with beer and a full pizza to yourself each night and expect to lose weight, so there's some personal responsibility involved. But if you're doing all the right things and are still stuck in a weight-loss rut, there could be some underlying physiological reasons why your weight just isn't coming off.

You have insulin resistance
When you eat, your blood sugar levels rise, and your body releases insulin to help your fat, muscle, and liver cells absorb the glucose. With insulin resistance, however, these cells don't respond properly to insulin, which leaves your blood sugar levels high, and puts your pancreas into overdrive trying to produce more insulin.

"If your insulin levels are high, you are not going to be able to lose weight," says Dr. Adam Splaver, clinical cardiologist and co-founder of NanoHealthAssociates. "Insulin actually causes sugar and simple sugars to be stored as fat." What's worse is that most people don't realize they're insulin resistant until after they've gained weight -- if left untreated, it can lead to type II diabetes.

While many people can remedy insulin resistance with certain medication and a diet low in sugar and simple carbohydrates, it's important to see your doctor and get your blood sugar levels tested to see if insulin resistance could in fact be the issue.

You're not getting quality sleep
In a perfect world, you would be getting six to eight hours of sleep a night. Any less, and you're opening yourself up to weight gain for a whole host of reasons, from craving junk food to not having enough energy to work out. But if you have a sleep disorder such as sleep apnea, you'll wake up several times throughout the night (usually without even realizing it), and shave off quality hours from your slumber.

"If you're sleep-deprived, you will not be able to lose weight," warns Dr. Adam Splaver, and that goes for those who chug coffee before a night on the town and those who think they're doing everything right. So if you consistently sleep the recommended hours but still wake up groggy and feel fatigued throughout the day, check with your doctor to get tested for sleep apnea.

You're too stressed out
Chronic, nagging stress seems to be the norm for most people, especially those who have approximately 17 decades to go on student loan payments. When you're stressed, your body churns out the stress hormone cortisol, which helps regulate blood pressure and fluid balance in times of need. The problem is, even if you're not in survival mode (i.e., a bear isn't chasing you in the woods), your body thinks it still needs to produce cortisol to fight off a screaming boss or looming credit card bill, and the hormone starts storing fat as an energy reserve. And not just anywhere; cortisol loves to put fat in the oh-so-flattering area of your belly, which is a riskier place to store it than, say, your arms or legs.

Dr. Splaver says high cortisol levels are common for people with a lot of stress in their lives, and when they're constantly elevated, it makes it hard to lose weight. Although you can't always get rid of the major stressors in your life, you can control how you handle them, which will make everything easier, not just weight loss.

You have a food intolerance
You might roll your eyes at your friend who swears he has a gluten sensitivity, but it's not just something bread-fearing health nuts shout into the night. A true food intolerance is what it sounds like: your body can't process a certain type of food. And when you eat something your body can't handle -- like gluten or dairy, which can actually be problematic for some people -- it triggers inflammation, which will make it pretty hard to lose weight, Dr. Splaver explains.

Chronic inflammation is like a constant fire burning inside your body trying to fight off low-level irritants, like those problem foods, and can get in the way of your weight loss. There are some foods you can eat to fight inflammation, but it's better to nip food intolerance in the bud. Try an elimination diet like the Whole30, and slowly reintroduce those foods after a month to see what could be the culprit.

There's something wrong with your thyroid
Your thyroid has a pretty important job. It releases thyroid hormones (go figure), which are responsible for temperature regulation, how energy is used, and making sure most of your organs are working properly. The thyroid also controls your metabolism, which means if it's not working properly, that will totally throw off how you convert the food you eat into energy, says Dr. Splaver.

Hypothyroidism, where your thyroid is underactive and doesn't make enough thyroid hormones, is associated with weight gain, colder body temperature, fatigue, and dry skin. These symptoms sound familiar? Go see an endocrinologist or your primary care doctor to get tested.

Your other hormones are out of whack
What makes men and women so different, besides every cliche that's been exploited on sitcoms and bad stand-up routines, are the differences in sex hormones. Men produce more testosterone, which is responsible for sperm production, sex drive, muscle size, and fat distribution. Women produce more estrogen, which is responsible for regulating menstrual cycles, cholesterol, and your mood, among other functions.

An imbalance of either is tied to weight gain; if women have too much estrogen, they can become insulin-resistant and store more fat. To make matters worse, extra fat tissue creates more estrogen, so it becomes an annoying cycle that can be hard to break. Men, on the other hand, can experience weight gain with too-low testosterone, since the hormone affects metabolism and muscle mass. Although hormones can be regulated with certain lifestyle changes, Dr. Splaver says people may need to take supplements to bring their hormone levels back to normal, which may help with weight loss.

The bottom line: unfortunately, losing weight isn't always as simple as calories in versus calories out. Anyone who tries to tell you otherwise is a liar who doesn't understand the struggle. These physiological roadblocks to weight loss could lead to more severe problems down the road, so make sure you see your doctor ASAP. He or she might finally be able to help you lose the weight once and for all.